Compact near-eye display optics for higher optical performance

ABSTRACT

Systems and methods are described for receiving image content from an emissive display toward a first filter stack, the first filter stack adapted to be oriented in a first direction from an optical axis of a first lens, and toward the first lens, transmitting the image content through a curved lens parallel to the optical axis of the first lens, wherein the curved lens transmits a portion of the image content to at least one optical element and to a second filter stack, the second filter stack being adapted to be oriented in a second direction from the optical axis of the first lens, and receiving the portion from the second filter stack and providing at least some of the portion to the first lens for viewing by a user.

TECHNICAL FIELD

This description generally relates to optical technology used ininteractive head-mounted display (HMD) devices.

BACKGROUND

Near-eye displays may be included in a wearable display, such as ahead-mounted display (HMD) device. An HMD device provides image contentin a near-eye display close to one or both eyes of a wearer. To generatethe image content on such a display, a computer processing system may beused. Such displays may occupy a wearer's entire field of view, or onlyoccupy a portion of the wearer's field of view.

SUMMARY

According to one general aspect, a system of one or more computers canbe configured to perform particular operations or actions by virtue ofhaving software, firmware, hardware, or a combination of them installedon the system that in operation causes or cause the system to performthe actions. One or more computer programs can be configured to performparticular operations or actions by virtue of including instructionsthat, when executed by data processing apparatus, cause the apparatus toperform the actions. One general aspect includes a computer-implementedmethod that includes receiving image content from an emissive displaytoward a first filter stack in which the first filter stack is adaptedto be oriented in a first direction from an optical axis of a firstlens, and toward the first lens. The method may include transmitting theimage content through a curved lens parallel to the optical axis of thefirst lens. The curved lens may transmit a portion of the image contentto at least one optical element and to a second filter stack. The secondfilter stack may be adapted to be oriented in a second direction fromthe optical axis of the first lens. The method may also includereceiving the portion from the second filter stack and providing atleast some of the portion to the first lens for viewing by a user. Insome implementations, the portion changes polarized handedness fromright hand circularly polarized to left hand circularly polarized uponpassing through the curved lens and the at least one optical element.

Implementations can include one or more of the following features, aloneor in combination with one or more other features. The first directionmay include an angle of about 5 to about 13 degrees off of a verticaloffset from the optical axis of the first lens and toward the firstlens. The second direction may include an angle of about 5 degrees offof the vertical offset from the optical axis of the first lens andtoward the first lens. In some implementations, the first filter stackand the second filter stack are parallel to the first lens and thecurved lens, the first lens being aligned on an axis common to thecurved lens and the emissive display.

In some implementations, the curved lens is composed of plastic andcoated with a beam splitter layer. In some implementations, the beamsplitter layer includes positive mirror surface configured to resolvedisplay pixels. In some implementations, the at least one opticalelement comprises two or more optical lenses adapted to further reduceoptical aberrations.

In some implementations, the first filter stack includes a first linearpolarizer coupled to a first quarter wave plate, the second filter stackincludes a second quarter wave plate coupled to a polarizing beamsplitter that is coupled to a second linear polarizer, and the curvedlens includes a plastic lens with a beam splitter coating, the curvedlens being disposed between the first filter stack and the second filterstack.

In another general aspect, a head-mounted display housing may include atleast one optical assembly including a curved beam splitter devicedisposed between a first filter stack and a second filter stack, animage projecting device adapted to be seated at a plurality of angleswithin the head-mounted display housing, and a first lens. The opticalassembly may be configurable to balance a field of curvature in responseto tilting the first filter stack or the second filter stack.

In some implementations, the image projecting device is seated at anangle selected based on a tilt angle associated with the first filterstack or the second filter stack. The tilt angle may be more than 5degrees and less than 25 degrees of a vertical offset from an opticalaxis of the first lens. In some implementations, tilting the firstfilter stack or the second filter stack results in modifying a field ofview associated with the head-mounted display housing, the modificationincluding moving image artifacts outside of the field of view. In someimplementations, the first lens is non-rotationally symmetrical. In someimplementations, the first lens provides a focal length of about 13millimeters to about 20 millimeters within the head-mounted displayhousing. In some implementations, the first lens is adapted to maintainimage magnification and focus in response to detecting movement of atleast one optical assembly.

In some implementations, the head-mounted display housing includes twooptical assemblies and each of the optical assemblies may be configuredto provide image content to the first lens in corresponding left andright eyepieces associated with the head-mounted display housing.

In some implementations, the head-mounted display housing furtherincludes a plurality of optical elements disposed between the firstfilter stack and the second filter stack. The plurality optical elementsmay be configured to decrease optical aberrations.

In another general aspect, a method includes receiving image contentfrom a display toward a first filter stack and transmitting a portion ofthe image content through a curved lens parallel to the optical axis ofa first lens. The portion of the image may be partially reflected andpartially transmitted after passing through the curved lens and to asecond filter stack.

Implementations can include one or more of the following features, aloneor in combination with one or more other features. In someimplementations, the partially transmitted portion changes polarizedhandedness from right hand circularly polarized to left hand circularlypolarized, and wherein the partially transmitted portion is transmittedthrough the second filter stack, and provided to the first lens forviewing by a user.

In some implementations, the first filter stack and the second filterstack are flat, non-curved elements. In some implementations, the firstfilter stack and the second filter stack are parallel to the first lensand the curved lens. The first lens may be aligned on an axis common tothe curved lens and the display. In some implementations, the curvedlens is composed of plastic and coated with a beam-splitting layerincluding a positive mirror surface configured to resolve displaypixels.

In some implementations, the first filter stack includes a first linearpolarizer coupled to a first quarter wave plate, the second filter stackincludes a second quarter wave plate coupled to a polarizing beamsplitter that is coupled to a second linear polarizer, and the curvedlens includes a plastic lens with a beam splitter coating, the curvedlens being disposed between the first filter stack and the second filterstack.

Other embodiments of this aspect include corresponding computer systems,apparatus, and computer programs recorded on one or more computerstorage devices, each configured to perform the actions of the methods.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example system for rendering imagecontent in a head-mounted display (HMD).

FIG. 2 is a block diagram depicting an example optical assembly.

FIG. 3 is a diagram depicting an example polarization path of lighttravelling through the optical assembly illustrated in FIG. 2.

FIG. 4 is a block diagram depicting an example hybrid optical assembly.

FIG. 5 is a diagram depicting an example polarization path of lighttravelling through the hybrid optical assembly illustrated in FIG. 4.

FIG. 6 is a block diagram of a variably tilted optical assembly.

FIG. 7 is a block diagram of another variably tilted optical assembly.

FIG. 8 is an example packaged optical assembly for housing the opticalassemblies described herein.

FIG. 9 is an example of a top down view of a packaged HMD device capableof housing optical assemblies described herein.

FIG. 10 is an example of a packaged HMD device capable of housing anoptical assembly in accordance with an embodiment described herein.

FIG. 11 is an example of a packaged HMD device capable of housing anoptical assembly in accordance with an embodiment described herein.

FIG. 12 is a flow chart diagramming one embodiment of a process for usewith the optical assemblies described herein.

FIG. 13 is a flow chart diagramming one embodiment of a process for usewith the optical assemblies described herein.

FIG. 14 is a flow chart diagramming one embodiment of a process for usewith the optical assemblies described herein.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Accessing virtual reality (VR) content generally includes having a userwear an HMD device that can be configured to function with a mobilecomputing device (or other display) inserted into the HMD device. SuchHMD devices can include optical componentry that provide magnification,polarization, filtering, and/or image processing for images provided bythe mobile computing device. The methods and systems described in thisdisclosure may include optical features for such HMD devices thatprovide the advantage of reducing the size of an optical assembly housedin an HMD device. Such a reduction of the optical assembly can allowreduction of the display space within the HMD device, thereby reducingthe size, weight, and moment of inertia of the HMD device when worn bythe user. A reduced size and weight of the HMD device may provide theadvantage of further integrating the user into a virtual realityenvironment because wearing a lighter weight and/or smaller device canreduce the awareness of wearing the HMD device while accessing thevirtual reality environment.

The systems and methods described in this disclosure may include usingoptical assemblies and optical methods to reduce HMD device thicknesswhile taking advantage of lens systems that interact and integrate wellwith mobile computing device displays. In some implementations, theoptical assemblies and methods can employ at least two flat polarizationfilter stacks (for at least one eyepiece or for each of a left and righteyepiece) to fold the optical path between a long focal lengthmagnifying lens and a display panel.

Such an assembly can significantly reduce the lens display space withinthe HMD device. For example, the lens display space can be reduced up toabout 60 percent to about 70 percent of typical lens display space usedby a mobile computing device-based HMD device. In one non-limitingexample, the lens display space may be reduced from about 39 millimetersto about 13 millimeters. In other examples, the lens display space maybe reduced from about 39 millimeters to about 13.5 millimeters. Inanother non-limiting example, the lens display space may be reduced fromabout 39 millimeters to about 12.48 millimeters. In another non-limitingexample, the lens display space may be reduced from about 45 millimetersto about 15.75 millimeters. In another non-limiting example, the lensdisplay space may be reduced from about 40 millimeters to about 16millimeters. In another non-limiting example, the lens display space maybe reduced from about 40 millimeters to about 13 millimeters.

Reducing the lens display space in this fashion can function to move theHMD device center of gravity closer to the head of the user wearing thedevice, thereby reducing the moment of inertia of the user. The reducedlens display space can additionally provide aesthetic advantagesresulting in a streamlined, low-profile HMD device.

The systems and methods described in this disclosure may utilize hybridoptical assemblies and optical methods to achieve a compact near-eyedisplay (e.g., within an HMD device) for virtual reality. Such a displaymay reduce the thickness of the HMD device while improving moment ofinertia and industrial design, similar to the other optical assembliesdescribed herein. The hybrid optical assemblies can include inlinestructures that employ additional optical elements between two or morefilter stacks. In one non-limiting example, a beam splitting layermanufactured on a surface of a curved lens may be housed between two ormore filter stacks. In some implementations, the optical elements in thehybrid optical assemblies may include a curved lens with a beam splittercoating as well as two or more optical lenses adapted to further reduceoptical aberrations and improve image quality. In general, the hybridoptical assemblies can provide the advantages of having lower opticalaberrations from many of the optical elements, less sphericalaberration, less astigmatism, and less coma. The hybrid opticalassemblies described herein may also include a positive mirror surface,which can allow a user to resolve smaller display pixels. In someimplementations, the hybrid optical assembly may be housed in an HMDdevice housing that is slightly larger than the non-hybrid opticalassemblies described herein. Increasing the HMD device housing for ahybrid optical assembly can reduce pupil swimming (i.e., reduce theeffect that occurs when an image displayed in an HMD device distorts asa user moves her eye around a lens provided in the HMD device). Thehybrid optical assemblies can also provide a balance of field curvatureas positive refractive elements may be used to balance the fieldcurvature of a concave mirror housed within the assembly of two opticalfilter stacks.

The systems and methods described in this disclosure may include usingvariably tilted optical assemblies within the HMD device. In one suchexample, a display panel for both a left and a right eye can be designedto be tilted such that the top of the displays are angled toward theeyes of the user and the bottom of the displays are angled away from theeyes of the user. In another example, one or both filter stacks within aparticular optical assembly (for each eyepiece) can be designed to beoriented and/or angled in a direction toward or away from the eyepiece.

Providing variably tilt-able components within an optical assembly forHMD devices may provide the advantage of increasing nose clearancewithout changing the shape of an HMD device. In addition, allowingtilt-able display panels may save a manufacturer design time and costwhile providing an improved image to the user. In some implementation,tilting one or more components can also provide a translational effectwhich can increase the center clearance between the two (i.e., left andright) display panels.

Referring to FIG. 1, a virtual reality (VR) system and/or an augmentedreality (AR) system may include, for example, an HMD device 102 orsimilar device worn by a user 103, on a head of the user, to generate animmersive virtual world environment to be experienced by the user. TheHMD device 102 may represent a virtual reality headset, glasses, one ormore eyepieces, or other wearable device capable of displaying virtualreality content. In operation, the HMD device 102 can execute a VRapplication (not shown) which can playback received and/or processedimages to a user.

FIG. 1 is a diagram that illustrates a system 100 with a userinteracting with content on a mobile computing device 104. In theexample shown in FIG. 1, the user may be accessing content (e.g.,images, audio, video, streaming content, etc.) via mobile computingdevice 104 to HMD device 102. In some implementations, one or morecontent servers (e.g., server 106) and one or more computer-readablestorage devices can communicate with the mobile computing device 104using a network 110 to provide the content to the mobile computingdevice 104, which may feed the content to HMD device 102. The contentcan be stored on the mobile computing device 104 or another computingdevice.

In the example implementation shown in FIG. 1, the user 103 is wearingthe HMD device 102 and holding mobile computing device 104. Movement ofthe user in the real world environment may be translated intocorresponding movement in the virtual world environment using sensorsand software on the mobile computing device 104. In someimplementations, the mobile computing device can be interfacedto/connected to the HMD device 102. In some implementations, the mobilecomputing device 104 can execute a VR application.

The mobile computing device 104 may interface with a computer-generated,3D environment in a VR environment. In these implementations, the HMDdevice 102 includes a screen and optical assemblies that include atleast a lens 112, a filter stack 114, and a filter stack 116. The filterstacks 114 and 116 will be described in detail throughout thisdisclosure. The filter stacks 114 and 116 may be included in opticalassemblies for each eyepiece in the HMD device 102. In someimplementations, other optical elements may be disposed between, coatedupon, or otherwise coupled or affixed to the filter stack 114 and/or thefilter stack 116.

The mobile computing device 104 may be a portable electronic device,such as, for example, a smartphone, or other portable handheldelectronic device that may be paired with, or operably coupled with, andcommunicate with, the HMD device 102 via, for example, a wiredconnection, or a wireless connection such as, for example, a Wi-Fi orBluetooth connection. This pairing, or operable coupling, may providefor communication and exchange of data between the mobile computingdevice 104 and the HMD device 102. Alternatively, a server device 106 orlocal computer 108 (or other device accessible by the user) may functionto control HMD device 102 via network 110.

In some implementations, the HMD device 102 can connect to/communicatewith the mobile computing device 104 (or other device 106, 108, etc.)using one or more high-speed wired and/or wireless communicationsprotocols (e.g., WiFi, Bluetooth, Bluetooth Low Energy (LE), UniversalSerial Bus (USB), USB 3.0, USB Type-C, etc.). In addition, or in thealternative, the HMD device 102 can connect to/communicate with themobile computing device using an audio/video interface such asHigh-Definition Multimedia Interface (HDMI). In some implementations,the content displayed to the user on the screen included in the HMDdevice 102 may also be displayed on a display device that may beincluded in device 106 and/or 108. This allows someone else to see whatthe user may be interacting with in the VR space.

In the example system 100, the devices 104, 106, and 108 may be a laptopcomputer, a desktop computer, a mobile computing device, or a gamingconsole. In some implementations, the device 104 can be mobile computingdevice that can be disposed (e.g., placed/located) within the HMD device102. The mobile computing device 104 can include a display device thatcan be used as the screen for the HMD device 102, for example. Devices102, 104, 106, and 108 can include hardware and/or software forexecuting a VR application. In addition, devices 102, 104, 106, and 108can include hardware and/or software that can recognize, monitor, andtrack 3D movement of the HMD device 102, when these devices are placedin front of or held within a range of positions relative to the HMDdevice 102. In some implementations, devices 104, 106, and 108 canprovide additional content to HMD device 102 over network 110. In someimplementations, devices 102, 104, 106, and 108 can be connectedto/interfaced with one or more of each other either paired or connectedthrough network 110. The connection can be wired or wireless.

In some implementations, the network 110 can be a public communicationsnetwork (e.g., the Internet, cellular data network, dialup modems over atelephone network) or a private communications network (e.g., privateLAN, leased lines). In some implementations, the mobile computing device104 can communicate with the network 110 using one or more high-speedwired and/or wireless communications protocols (e.g., 802.11 variations,WiFi, Bluetooth, Transmission Control Protocol/Internet Protocol(TCP/IP), Ethernet, IEEE 802.3, etc.).

The system 100 may include electronic storage. The electronic storagecan include non-transitory storage media that electronically storesinformation. The electronic storage may be configured to store capturedimages, obtained images, pre-processed images, post-processed images,etc.

FIG. 2 is a block diagram depicting an example optical assembly 200.

The optical assembly 200 may be installed as part of an HMD deviceintended for accessing virtual reality content. As shown in FIG. 2, aneye 202 of a user is simulated to the left of the optical assembly 200and a display panel 204 is shown to the right of the optical assembly200. In some implementations, an optical assembly 200 may be includedfor each of a left and right eyepiece. In some implementations, theoptical assembly 200 may be included in a single eyepiece.

The optical assembly 200 includes the display panel 204, a first flatfilter stack 206 that includes a beam splitter (not shown), a secondflat filter stack 208, and a lens 210. The optical assembly 200 canfunction to fold the optical path of light presented by display panel204 and through the filter stacks 206 and 208. In this example, examplefolded optical paths are shown by paths 212, 214, and 216.

In one non-limiting example, the optical assembly 200 can be installedin a system that includes an interactive HMD device (e.g., device 102)worn by a user (e.g., user 103). The interactive HMD device may beadapted to house an image projecting device (e.g., device 104) and anoptical assembly (e.g., 200). In some implementations, the imageprojecting device includes a display on a mobile computing device. Insome implementations, the display may be an organic light emittingdisplay (OLED). In other implementations, the display may be a liquidcrystal display (LCD). In yet other implementations, the display may bea reflective display that includes a liquid crystal on silicon (LCOS)display. Other display technologies may be used, as described in detailbelow.

The optical assembly 200 may include at least one refracting lens 210.In some implementations, the at least one refracting lens 210 may bedesigned to provide a focal length of about 30 millimeters to about 50millimeters, while the distance between the lens and the display may beabout 13 millimeters to about 20 millimeters due to the optical foldingof the two filter stacks 206 and 208. In some implementations, theoptical assembly 200 includes a plurality of refracting lenses or lensarrays.

An example assembly of the first filter stack 206 may include a firstlinear polarizer and a beam splitter layer applied as a coating to afirst quarter wave plate within the assembly (shown in detail withrespect to FIG. 3). The first filter stack 206 may be operable to filterand split light received from the image projecting device. In someimplementations, the quarter wave plates can be designed to functionwell in broadband to provide a constant phase shift independent of thewavelength of light that is used. This wavelength independence may beachieved by using two different birefringent crystalline materials. Therelative shifts in retardation over the wavelength range (i.e.,dispersion) can be balanced between the two materials used. The secondfilter stack 208 may include a quarter wave plate, a polarizing beamsplitter, and a linear polarizer within the assembly (shown in detailwith respect to FIG. 3). The second filter stack 208 may be operable tofold an optical path between the at least one refracting lens 210 andthe image projecting device (e.g., mobile computing device 104).

In some implementations, the optical assembly 200 also includes adisplay panel adapted to receive image content from the image projectingdevice (e.g., mobile computing device 104). In some implementations, theoptical assembly 200 also includes at least one processor for handlingimage content for display on the image projecting device. In particular,as described above with respect to FIG. 1, image content can be providedby one or more processors, computers, or other resources, and can bedisplayed, stored, and/or modified using image projecting device (e.g.,mobile computing device 104, etc.).

FIG. 3 is a diagram depicting an example polarization path 300 of lighttravelling through the optical assembly 200 illustrated in FIG. 2. Here,the filter stacks 206 and 208 are shown disposed between the displaypanel 204 and the lens 210.

In one non-limiting example, the first filter stack 206 is coupled tothe second filter stack 208 and configured into a stacked arrangementwith other components. One such example of a stacked arrangement mayinclude a first linear polarizer 302 that is adjacent to the displaypanel 204 and stacked adjacent to a first quarter wave plate 304. Thefirst quarter wave plate 304 is stacked or coated with a beam splitterlayer 306, which is stacked beside a second quarter wave plate 308 on afirst side of the plate 308. A second side of the second quarter waveplate 308 is stacked beside a polarizing beam splitter 310, which isstacked beside a second linear polarizer 312. The second linearpolarizer 312 is adjacent to the at least one refracting lens 210.

In some implementations, the beam splitter layer 306 includes apartial-mirror coating on the first filter stack 206. The beam splitterlayer 306 may be operable to split light beams/rays with a splittingratio of about 50 percent. In some implementations, the beam splitterlayer 306 may perform with a beam splitting ratio of about 50 percentand can have a maximum transmission of about 25 percent if the displayis linearly polarized or about 12.5 percent if the display isunpolarized. In some implementations, the beam splitter layer 306 is notincluded in the first filter stack 206 and is instead a standalonedevice positioned between filter stack 206 and filter stack 208.

In some implementations, the second filter stack 206 is configuredwithout the linear polarizer 302 in the event that the image projectingdevice includes a non-emissive display, such as an LCD display. Thelinear polarizer 302 may be excluded, for example, because an LCDdisplay generally provides linearly-polarized output.

In some implementations, the linear polarizer 312 in the filter stack208 is an optional component included so that the scattered light from auser's face (i.e., illuminated by the display light) is not reflecteddirectly by the polarizing beam splitter 310. Such reflections maynegatively affect a viewing experience and accordingly, includingelements to deter this provide the user an improved viewing experience.

The components shown in FIGS. 2 and 3 may provide any number of possiblepolarization paths when light is introduced to one or more of thecomponents. One example polarization path 300 may include the displaypanel 204 receiving 320 emitted light (from mobile computing device 104)to be linearly polarized [y] by linear polarizer 302. The light maybecome circularly-polarized [RHCP1] after passing through thequarter-wave plate 304, which may be placed at 45-degree angle. Forexample, the first quarter wave plate may be seated at about 45 degreesoff a vertical that corresponds with the longitudinal edge of the firstfilter stack 206. The light [RHCP2] is then partially reflected [RHCP3]to [y1] to [y2] by the beam splitter 306, which changes the handednessof its circular polarization. The light [LHCP] can be passed to thequarter-wave plate 308, which rotates the circularly-polarized light[x1] back to linearly-polarized.

The linearly-polarized light, which is orthogonal to the passing stateof the polarizing beam splitter 310, can be reflected [x2] by and becomecircularly-polarized again after passing back through the quarter waveplate 308. After passing through the quarter wave plate 308 the thirdtime (at point 314 [x1]), the light becomes linearly-polarized, whichcan be parallel to the passing state of the polarizing beam splitter310. The transmitted light [x3], after passing through another optionallinear polarizer 312, can be refracted by a lens/group of lenses 210 toform a virtual image to be presented to an eyepiece of an HMD device andthe eye of the user.

Although the components described throughout this disclosure may beshown and/or described as encapsulated/connected to other components,each component can be adhesively bound to adjacent components.Alternatively, each component can be mechanically connected, orfrictionally bound to adjacent components. In other implementations,none of the components are bound or connected, but may function togetheras a unit housed in an assembly. In some implementations, portions ofthe components may be coated, while other portions remain uncoated. Lensdevices shown throughout this disclosure may be standalone or integratedinto a manufactured assembly. In addition, although only one lens isshown in particular diagrams, multiple lenses can be substituted. Inaddition, when one optical assembly is depicted, additional opticalassemblies may be included in an HMD device. For example, opticalassemblies can be duplicated with the HMD device to provide one opticalassembly for each eyepiece.

By way of a non-limiting example, the filter stack 208 may be astandalone piece or may be bonded to the front refracting lens (or groupof lenses). Similarly, the filter stack 206 may be a stand-alone pieceor an integrated layer of the display panel 204. In someimplementations, a filter stack configuration includes the axes of thelinear polarizer 302 and the linear polarizer 312 being orthogonal.Similarly, the axes of the first quarter wave plate 304 and the secondquarter wave plate 308 may be orthogonal.

FIG. 4 is a block diagram depicting an example hybrid optical assembly400. The hybrid optical assembly 400 may include one or more opticalelements in between two filter stacks 406 and 410. The hybrid opticalassembly 400 may additionally place a beam splitting layer on a curvedsurface of a lens inserted between the two filter stacks 406 and 410.One advantage to using the hybrid optical assembly 400 may includeproviding lower optical aberrations from included optical elements andthe use of positive mirror surface, which can allow a viewer to resolvesmaller display pixels.

In some implementations, the display space within an HMD device housingthe hybrid optical assembly 400 may provide telecentricity allowingimproved focus adjustment when or if a display panel is shifted axially.In this configuration, the image magnification and distortion may remainconstant when one or more of the display panels shift axially for focusadjustment.

As shown in FIG. 4, an eye 402 of a user is simulated to the left of theoptical assembly 400, while a display panel 404 is shown to the right ofthe optical assembly 400. The optical assembly 400 includes a first flatfilter stack 406, a curved lens 408 that includes a beam splitter layerbuilt in (not shown), a second flat filter stack 410, and a lens 412.

In some implementations, the lens 412 may be included in the opticalassembly for each of the left and right eyepiece. The lens 412 may bedisposed in the HMD device adjacent to the filter stack 410 and adaptedto receive image content originating at the image projectingdevice/mobile computing device and through the optical assembly towardthe filter stack 410.

The optical assembly 400 can function to fold the optical path of lightpresented by display panel 404 and through the filter stacks 406 and410. In this example, example folded optical paths are shown by paths414, 416, and 418. In the depicted example, the curved lens 408 mayinclude a beam splitter coating including a positive mirror surfaceconfigured to resolve display pixels. The lens 408 may be disposed suchthat the concave side faces the filter stack 410 and the convex sidefaces filter stack 406. In some implementations, the optical assembly400 may be telecentric when the average angle of ray bundles on thedisplay surface is close to perpendicular.

FIG. 5 is a diagram depicting an example polarization path 500 of lighttravelling through the hybrid optical assembly 400 illustrated in FIG.4. Here, the filter stacks 406 and 410 are disposed between the displaypanel 404 and lens 412.

In one non-limiting example, the first filter stack 406 is coupled tothe second filter stack 410 and configured into a stacked arrangementwith other components. One such example of a stacked arrangement mayinclude a first linear polarizer 502 that is adjacent to the displaypanel 404 and next to a first quarter wave plate 504. The first quarterwave plate 504 is stacked adjacent to a curved lens 408, which isstacked adjacent to a second quarter wave plate 506. The second quarterwave plate 506 is stacked adjacent to a polarizing beam splitter 508,which is stacked adjacent to a second linear polarizer 510. The secondlinear polarizer 510 is adjacent to the at least one lens 412.

In some implementations, the lens 412 may be a refracting lens. In someimplementations, multiple lenses or lens arrays may take the place oflens 412.

In general, the lenses 408 and 412 may be non-rotationally symmetrical.Non-rotationally symmetrical lenses 408 and 412 can be beneficialwhenever the system is no longer rotationally symmetric. For example, asshown in the hybrid optical assembly 700 of FIG. 7, the system may nolonger be rotationally symmetric because the lenses are decenteredand/or tilted optically. In another example, the system may no longer berotationally symmetric when the display is curved differently in twoorthogonal meridians (e.g., cylinder, saddle-shape, etc.). In someimplementations, using non-rotationally symmetrical lenses can providethe advantage of successfully balancing the aberrations to achieve auniform image quality across the field of view.

The components shown in FIGS. 4 and 5 may provide any number of possiblepolarization paths of light traveling through the components. Oneexample polarization path 500 may include the display panel 404 emittinglight 520 to be linearly polarized by linear polarizer 502. The light[y] may become circularly-polarized [RHCP1] after passing through thequarter-wave plate 504, which may be placed at 45-degree angle. Forexample, the quarter wave plate 504 may be seated at about 45 degreesoff a vertical that corresponds with the longitudinal edge of the firstfilter stack 406. The light [RHCP2] may be partially reflected [RHCP3]by the curved lens 408, which can change the handedness of its circularpolarization from right to left [LHCP]. The light can be passed to thequarter-wave plate 506, which can rotate the circularly-polarized lightback to linearly-polarized.

The linearly-polarized light, which may be orthogonal to the passingstate of the polarizing beam splitter 508, may be reflected by andbecome circularly-polarized again [y1 ]to [y2 ]to [x1] after passingback through quarter wave plate 506. After passing through quarter waveplate 506 the third time (at location 512), the light [x2] may becomelinearly-polarized, which may be parallel to the passing state of thepolarizing beam splitter 508. The transmitted light [x3], after passingthrough another optional linear polarizer 510, may be refracted by alens/group of lenses 412 and may form a virtual image to be presented toan eyepiece of an HMD device and the eye of the user.

FIG. 6 is a block diagram of a variably tilted optical assembly 600. Thevariable tilt may refer to tilting or reorienting of one or more of thefilter stacks within the optical assembly 600. Alternatively, thetilting may refer to being able to tilt a display panel housed nearfilter stacks within the optical assembly 600. In some implementations,the tilting may be based on an angular relationship between one or morefilter stacks to the display panel and/or to the lens.

As shown in FIG. 6, an eye 602 of a user is simulated to the left of theoptical assembly 600 and a display panel 604 is shown to the right ofthe optical assembly 600. The optical assembly 600 includes the displaypanel 604 and a first flat filter stack 606 that includes a beamsplitter (not shown), a second flat filter stack 608. The opticalassembly 600 also includes a lens 610 adjacent to the filter stack 608.The optical assembly 600 can function to fold the optical path of lightpresented by display panel 604 and through the filter stacks 606 and608. In this example, example folded optical paths are shown by paths612, 614, 616, 618, and 620.

Optical assembly 600 may include components described with respect toFIGS. 2 and 3. As such, optical assembly 600 may provide examplespertaining to a tilt-able optical assembly 200. In this example, bytilting the display panel 604 at an angle 622 relative to the opticalaxis of lens 610, a variable space can be created between surfaces of afront polarization filter stack (e.g., filter stack 608) and a beamsplitting surface coated on filter stack 606. In operation, the displaypanel for each of a left and right display area can be tilted so thatthe corners or edges of the display panel are further outward which mayprovide the advantage of significantly increasing the nose clearance,without the need to make a custom shaped HMD display. The tilting mayadditionally have a translational effect, which increases the centerclearance between the two display panels (for each eye). In someimplementations, tilting the two displays can also help make the HMDdevice form better to the face of a user, ultimately allowing a compactand appealing-looking industrial design.

As shown, two flat filter stacks 606 and/or 608 may also be adjusted(i.e., tilted) to form an angle 624 in which the display panel 604 canbe moved to match such an angle. In some implementations, the filterstack 606 may be adjusted to form an angle 626 in which the displaypanel 604 can be moved to match such an angle.

The filter stacks 606 and 608 may be part of a near-eye display systemassembly for an HMD device. For example, the stacks 606 and 608 alongwith lens 610 and display panel 604 can be housed in a head-mounteddisplay device worn by a user. The filter stacks 606 and 608 may bepieces of one or more optical assemblies that can provide image contentto each of a left and right eyepiece in the HMD device. The flat filterstack 606 may be operable to be oriented in a first direction (e.g.,from zero to about 12.5 degrees toward an eyepiece in an HMD device).The filter stack 606 may include at least one surface coated with a flatbeam splitting layer. The beam splitting layer may be faced away fromdisplay panel 604 and toward filter stack 608. The flat filter stack 608may be operable to be oriented in a second direction (e.g., from zero toabout 12.5 degrees toward an eyepiece in an HMD device).

In some implementations, the filter stack 606 may be bonded directly tothe display panel 604 to provide zero degree filter angles. In someimplementations, the filter stack 608 may be bonded directly to thedisplay panel 604 to provide zero degree filter angles.

In some implementations, the filter stack 606 may be adapted to beoriented in the first direction at an angle from about zero to about12.5 degrees from the normal direction to the plane of the displaypanel. The flat filter stack 608 may be adapted to be tilted in thesecond direction at an angle from about zero to about 12.5 degrees fromthe normal direction to the plane of the display panel. One or bothreorientations/tilts may occur in response to tilting the display panelfrom about zero to about 25 degrees from the normal direction to theplane of a bottom edge of the head-mounted display device such that thedisplay panel is seated perpendicular to the optical axis of the neareye display system.

The selected first and second angles may pertain to one another and maybe selected based on an angle that the display panel is tilted. In oneexample, the display 604 is tilted and housed in the HMD device at anangle selected by a user. The display panel may be adapted to beoriented in the second direction, for example.

In general, tilting the display panel 604 may include seating thedisplay panel 604 within and perpendicular to a base of the HMD deviceand angling a top edge of the display panel 604 toward the opticalassembly (i.e., toward either or both of filter stack 606 and 608)corresponding to each of the left and right eyepiece. In general, theoptical assembly includes at least one fixed lens for each of the leftand right eyepiece. In some implementations, the at least one fixed lensfor each of the left and right eyepiece is disposed in the HMD deviceadjacent to the flat filter stack 608 and adapted to receive imagecontent originating at the image projecting device and through theoptical assembly toward the flat filter stack 608.

In some implementations, titling the display panel 604 may result inmodifying a field of view of the near-eye display system by moving imageartifacts outside of the field of view. Such a modification can functionto ensure that light that ghost images, created by stray light withinthe optical assembly, can be comfortably out of the line of sight of auser wearing the HMD device. The display panel 604 may additionally betilted to maintain image plane focus for a user wearing the HMD device.

In some implementations, the filter stacks 406 and 410 are adapted tomaintain a relationship to one another in order to maintain an opticalaxis perpendicular to the object plane to keep the optical systemon-axis. For example, in system 400, the tilt angle of the display panelmay be twice a relative tilt angle between the two flat filters. In onenon-limiting example, the filter stacks 406 and 410 may be adapted to betilted from zero to about 12.5 degrees in response to titling thedisplay panel 604 from about zero to about 25 degrees.

FIG. 7 is a block diagram of another variably tilted optical assembly700. Optical assembly 700 may include components described with respectto FIGS. 4 and 5. As such, optical assembly 700 may provide examplespertaining to a tilt-able optical assembly 400.

As shown in FIG. 7, an eye 702 of a user is simulated to the left of theoptical assembly 700, while a display 704 is shown to the right of theoptical assembly 700. The optical assembly 700 includes a first flatfilter stack 706, a curved lens 708, a second flat filter stack 710, anda lens 712. The optical assembly 700 can function to fold the opticalpath of light presented by display 704 and through the filter stacks 706and 710, and curved lens 708. In this example, example folded opticalpaths are shown by paths 714, 716, 718, 720, 722, 724, and 726. In someimplementations, the optical assembly 700 may be telecentric when theaverage angle of ray bundles on the display surface is close toperpendicular.

The optical assembly 700 pertains to the hybrid optical assembliesdescribed here. These assemblies may include tilted-image variants. Thecurved lens 708 may be composed of plastic and coated with a beamsplitter layer. The optical assembly 700 may be housed in an HMD device.The HMD device may include at least one of optical assembly 700. Opticalassembly 700 can, for example, include a curved beam splitter devicedisposed between a first filter stack and a second filter stack. Theoptical assembly may also include a removable image projecting deviceadapted to be seated at a number of different angles within the HMDdevice. In some implementations, the display panels seated between theimage projecting device and the first filter stack may be seated at anumber of different angles within the HMD device in response to tiltingthe first filter stack or the second filter stack.

In some implementations, the optical assembly 700 may be configurable tobalance a field of curvature in response to tilting the first filterstack or the second filter stack. In system 700, there may be noparticular set relationship between filter stacks. The tilt relationshipmay depend on variables including, but not limited to the curvature ofthe surface with the beam splitter coating, the location of beamsplitter, the location of the filter stacks, etc.

In an example, at least one display panel may be seated at an angleselected based on an orientation associated with the first filter stackor the second filter stack. The orientation may include a tilting ofmore than about 5 degrees and less than about 25 degrees of a verticaloffset from an optical axis of the lens. In some implementations,tilting the first filter stack or the second filter stack results inmodifying a field of view associated with the head-mounted displayhousing, the modification including moving image artifacts outside ofthe field of view.

In some implementations, the HMD device may include two opticalassemblies, each configured to provide image content to the lens incorresponding left and right eyepieces associated with the HMD device.For example, each optical assembly may be configured to provide imagecontent through separate left and right eye lenses. In someimplementations, the lenses are adapted to maintain image magnificationand focus in response to detecting movement of at least one of theoptical assemblies. For example, if one or both stacks in an opticalassembly movies, the lens associated with such stacks can accommodatethe movement without loss of image magnification and focus level. Insome implementations, the optical assembly 700 includes a number ofoptical elements disposed between the first filter stack and the secondfilter stack. The optical elements may be configured to decrease opticalaberrations.

FIG. 8 is an example packaged optical assembly 800 for housing theoptical assemblies described herein. The optical assembly 800 includes ahousing 802 with a lens 804 seated within the housing. The internalcomponents of packaged assembly 800 may include the combination ofcomponents shown in FIG. 3 or FIG. 5 or the tilted variations of suchcomponents. Example dimensions of the assembly 800 include a width 806of about 2 to about 3 inches and a length 808 of about 2 to about 3inches. The depth 810 of the assembly 800 may be about one to about 2.5inches.

In some implementations, exact depth can vary based on including or notincluding particular filter layers, as described throughout thisdisclosure. In some implementations, two of the assembly 800 may befitted into an HMD device, each inserted to provide filtering and opticsto each of a left and right eyepiece in the HMD display.

The lens 804 may be a refracting lens or other lens configurable toprovide high-performance focus and magnification for a HMD device. Insome implementations, the housing 800 may be designed to fit multiplelenses or a lens array instead of single lens 804.

In some implementations, the lens 804 may have a diameter 812 of about 1to about 1.5 inches. In some implementations, the lens 804 may have adiameter 812 of about 1.5 inches to about 2.5 inches. In yet otherimplementations, the lens 804 may have a diameter 812 of about 1 inch toabout 2 inches.

Although the depicted assembly 800 is depicted square with possiblemodifications to make a rectangular shaped assembly, other shapes arepossible. For example, the filter stacks described herein can be made tofit a circularly shaped housing intended for seating into the HMDdevice. In some implementations, the filter stacks described herein canbe made to fit an angular-sided assembly including, but not limited to atriangle, a rhombus, a hexagon, an octagon, etc.

FIG. 9 is an example of a top down view 900 of a packaged HMD device 904capable of housing one or more of the optical assemblies describedherein. The HMD device 904 can be fitted with a mobile computing device(i.e., mobile phone) adapted to playback movie content, virtual realitycontent, or other curated content displayable on the screen of themobile computing device. In general, HMD devices can take advantage ofmobile phone display technologies, which provide high-resolution, sizingof two to about three inches wide per channel at a focal lens length ofabout 35 millimeters to about 45 millimeters, as shown by typical HMDsize at dotted line 902. The HMD device 904 can provide additionaladvantages by using one or more of the optical assemblies describedherein (e.g., optical assemblies shown in FIGS. 1-11). Using suchoptical assemblies, the HMD device 904 can effectively reduce the focallength of the lens from a typical length (i.e., about 30-50 millimeters)to about 12 to about 25 millimeters, as shown by thickness 906. This canprovide the advantage of being able to shrink the HMD device includingallowing manufacturers to design a stream-lined device that a user 908can fit closer to her face. In some implementations, the opticalassemblies described herein can reduce the lens display space up toabout 67 percent from typical HMD devices. Such a reduction can provideadvantages such as moving the HMD device center of gravity closer to thehead of the user, reducing the moment of inertia, and providing acompact, appealing-looking virtual reality HMD device, such as device904. In one example implementation, the HMD device may be reduced inprofile between about 15 and 25 millimeters based on the reduced focallength.

To avoid having to design a short focal length magnifier while reducingthe HMD device thickness/profile/focal length, the optical assembliesdescribed herein can employ two flat polarization filter stacks to foldthe optical path between a long focal length magnifying lens and thedisplay panel. The optical assemblies described herein can be providedfor each eye. In general, the flat filter stacks described throughoutthis disclosure do not provide optical magnification, and are thin suchthat the stacks contribute minimally to optical aberrations.

FIG. 10 is an example of a packaged HMD device 1000 capable of housingthe optical assemblies described herein. The HMD device 1000 can befitted with a mobile computing device (i.e., mobile phone) adapted toplayback movie content, virtual content, or other curated contentdisplayable on the screen of the mobile computing device.

In one non-limiting example, the HMD device 1000 can be fitted with atleast two optical assemblies, for example, one assembly for eacheyepiece of the HMD device 1000. In one example arrangement, the opticalassemblies can include a first and second filter stack, at least onerefracting lens, and a display panel. The first filter stack may beadjacent and/or attached on a first side to a display panel thatreceives light from the mobile computing device. The first filter stackmay include a first linear polarizer nearest the display panel and afirst quarter wave panel attached to the linear polarizer. The side ofthe linear polarizer not attached to the first quarter wave panel may becoated with a beam splitter layer. A second filter stack may be adjacentand/or attached on the beam splitter layer to the second filter stack.The second filter stack may include a second quarter wave plate attachedor adjacent to the beam splitter layer on a first side and attached to apolarizing beam splitter on the second side. The polarizing beamsplitter may be attached to a first side of a second linear polarizer.The second side of the second liner polarizer may be attached oradjacent to the at least one refracting lens or lens array.

In another example, the optical assemblies may include a first filterstack coupled to a second filter stack and configured into a stackedarrangement with other components. One such example of a stackedarrangement may include a first linear polarizer that is adjacent to adisplay panel and after a first quarter wave plate. The first quarterwave plate is stacked after a curved lens functioning as a beamsplitter, which is stacked after a second quarter wave plate. The secondquarter wave plate is stacked after a polarizing beam splitter, which isstacked after a second linear polarizer. The second linear polarizer isadjacent to the at least one lens or lens array.

As shown in FIG. 10, the user 1002 may be wearing HMD device 1000 andaccessing content. The front profile 1004 may be fitted closer to thehead of the user 1002 because slim optical assemblies described hereincan be fitted within the smaller housing of HMD 1000. A dotted line 1006depicts a typical HMD housing profile.

The HMD device 1000 may be low-profile and adapted to reduce a focallength by using optical assemblies 200 or 400 within the device, forexample. The filter stacks utilized in such assemblies can be flat andadapted to fold the optical path between a long focal length magnifyinglens and a display panel.

FIG. 11 is an example of a packaged HMD device 1100 capable of housingthe optical assemblies described herein. Similar to the above examples,the HMD device 1100 can be fitted with a mobile computing device (i.e.,mobile phone) adapted to playback movie content, virtual content, orother curated content displayable on the screen of the mobile computingdevice. In one non-limiting example, the HMD device 1100 can be fittedwith at least two optical assemblies, for example, one assembly for eacheyepiece of the HMD device 1100. In some implementations, the opticalassemblies may be particularly designed to be tilt-able, and thus afront panel 1104 may be designed with a backward tilt toward a foreheadarea of a user 1102.

As shown in FIG. 11, the user 1102 may be wearing HMD device 1100 andaccessing content. The HMD device 1100 may be low-profile and tilted asshown by front facing 1104 in order to reduce a focal length by usingoptical assemblies 600 or 700 within the device, for example. A dottedline 1106 depicts a typical HMD housing profile. The filter stacksutilized in such assemblies can be flat and adapted to fold the opticalpath between a long focal length magnifying lens and a display panel.The lens display space may be about 13 millimeters to about 20millimeters.

In one example, the optical assemblies can include a first and secondfilter stack, at least one refracting lens, and a display panel. In oneexample arrangement, the first filter stack may be adjacent and/orattached on a first side to a display panel that receives light from themobile computing device. The first filter stack may include a firstlinear polarizer nearest the display panel and a first quarter wavepanel attached to the linear polarizer. The side of the linear polarizernot attached to the first quarter wave panel may be coated with a beamsplitter layer. A second filter stack may be adjacent and/or attached onthe beam splitter layer to the second filter stack. The second filterstack may include a second quarter wave plate attached or adjacent tothe beam splitter layer on a first side and attached to a polarizingbeam splitter on the second side. The polarizing beam splitter may beattached to a first side of a second linear polarizer. The second sideof the second liner polarizer may be attached or adjacent to the atleast one refracting lens or lens array.

In another example, the optical assemblies may include a first filterstack coupled to a second filter stack and configured into a stackedarrangement with other components. One such example of a stackedarrangement may include the first filter stack that includes a firstlinear polarizer stacked between a display panel and a first quarterwave plate. The first quarter wave plate may be stacked between thefirst linear polarizer and a beam splitter. The second filter stack mayinclude a polarizing beam splitter stacked between a second quarter waveplate stacked after the beam splitter and a polarizing beam splitter.The polarizing beam splitter may be stacked between the second quarterwave plate and a second linear polarizer. The second linear polarizermay be adjacent to at least one refracting lens or lens array.

FIG. 12 is a flow chart diagramming one embodiment of a process 1200 foruse with the optical assemblies described herein. The process 1200 mayinclude filtering light for a near-eye display system in an HMD device.The optical assemblies may include a first filter stack and a secondfilter stack that are flat, non-curved elements, which do not provideoptical magnification.

The process 1200 may include receiving 1202 a light beam at a displaypanel and from a display that directs light through a first linearpolarizer in a first filter stack. For example, the display panel may bedisposed within an HMD device to receive image content from a mobilecomputing device (or from content stored on a processor associated withthe HMD device). The first linear polarizer may transmit the light beaminto a first quarter-wave plate (also in the first filter stack). Thelight beam may become circularly polarized in a first direction andfurther transmitted through a beam splitter (in the first filter stack).The beam splitter may be operable to transmit (1204) at least some ofthe light beam to a second quarter wave plate in a second filter stack.In some implementations, the beam splitter includes a partial-mirrorcoating on the first filter stack and performs with a beam splittingratio of about 50 percent. In some implementations, the beam splittermay have a maximum transmission of about 25 percent of the light(transmitted from the beam splitter to the display) if the display islinearly polarized. In the event that the display is unpolarized, thelight may be transmitted with a maximum transmission of about 12.5percent (transmitted from the beam splitter to the display) if thedisplay is unpolarized.

The process 1200 may include transmitting (1206) a first portion of thelight beam from the second quarter wave plate to a polarizing beamsplitter (in the second filter stack) in order to transform the firstportion into a linearly polarized light beam. In some implementations,the polarizing beam splitter is operable to reflect (1208) a secondportion of the linearly polarized light beam through the second quarterwave plate back to the beam splitter. In such an example, the secondportion may become circularly polarized in a second direction afterreflecting off of the beam splitter. In such an example, the firstdirection may be a right hand circularly polarized (RHCP) and the seconddirection may be left hand circularly polarized (LHCP).

The process 1200 may include transmitting (1210) the second portion fromthe beam splitter through the second quarter wave plate and through thepolarizing beam splitter and through a second linear polarizer in thesecond filter stack. In addition, the process 1200 may includetransmitting (1212) the second portion through at least one lens toprovide a refracted image to an eyepiece of the near-eye display system.

In some implementations, the first portion of the light beam isorthogonal to a passing state of the polarizing beam splitter and thesecond portion of the light beam is parallel to the passing state of thepolarizing beam splitter. In some implementations, at least some of thelight beam from the display is passed into the first quarter wave platefrom the first linear polarizer, wherein the first quarter wave plate isseated at about 45 degrees off a vertical in which the verticalcorresponds to a longitudinal edge of the first filter stack.

In some implementations, the axes of the first linear polarizer and thesecond linear polarizer are orthogonal and the axes of the first quarterwave plate and the second quarter wave plate are orthogonal.

In some implementations, the display is an emissive display andcomprises an organic light emitting diode (OLED) display. In someimplementations, the display is a non-emissive display and comprises aliquid crystal display (LCD) display.

FIG. 13 is a flow chart diagramming one embodiment of a process 1300 foruse with the optical assemblies described herein. The process 1300 mayinclude receiving (1302) image content from an emissive display toward afirst filter stack. In this example, the first filter stack is adaptedto be oriented in a first direction from the optical axis of a firstlens. In some implementations, the first filter stack may be tiltedtoward the first lens.

The process 1300 may include transmitting (1304) the image contentthrough a curved lens parallel to the optical axis of the first lens.The curved lens may transmit a portion of the image content to at leastone optical element and to a second filter stack. The second filterstack may be adapted to be oriented in a second direction from theoptical axis of the first lens. In one example, the first directionincludes about 5 to about 13 degrees off of a vertical offset from theoptical axis of the first lens (and toward the first lens) while asecond direction includes about zero to about 5 degrees off of thevertical offset from the optical axis of the first lens (and away fromthe first lens). In one example, the first filter stack may be tiltedtoward an eyepiece in the HMD device at about 3 degrees while the secondfilter stack is also tilted toward the eyepiece in the HMD device atabout 3 degrees. In another example, the first filter stack may betilted toward an eyepiece in the HMD device at about 5 degrees while thesecond filter stack is tilted toward the eyepiece in the HMD device atabout 10 degrees. In another example, the first filter stack may betilted toward an eyepiece in the HMD device at about 13 degrees whilethe second filter stack is tilted toward the eyepiece in the HMD deviceat about 10 degrees. In another example, the first filter stack may betilted toward an eyepiece in the HMD device at about 10 degrees whilethe second filter stack is also tilted toward the eyepiece in the HMDdevice at about 10 degrees. In yet another example, the first filterstack may be tilted away from an eyepiece in the HMD device at about 2degrees while the second filter stack is tilted toward the eyepiece inthe HMD device at about 2 degrees.

The process 1300 may include receiving (1306) the portion from thesecond filter stack and providing at least some of the portion to thefirst lens for viewing by a user. The portion changes polarizedhandedness from right hand circularly polarized to left hand circularlypolarized upon passing through the curved lens and the at least oneoptical element.

In some implementations, the first filter stack and the second filterstack are parallel to the first lens and the curved lens. The first lensmay be aligned on an axis common to the curved lens and the emissivedisplay.

In some implementations, the curved lens is composed of plastic andcoated with a beam splitter layer. The beam splitter layer may include apositive mirror surface configured to resolve display pixels.

In some implementations, the process 1300 may further include an opticalassembly that includes the first filter stack having a first linearpolarizer coupled to a first quarter wave plate. The optical assemblymay also include the second filter stack having a second quarter waveplate coupled to a polarizing beam splitter that is coupled to a secondlinear polarizer. The optical assembly may also include the curved lenshaving a plastic lens with a beam splitter coating. The curved lens maybe disposed between the first filter stack and the second filter stack.

FIG. 14 is a flow chart diagramming one embodiment of a process 1400 foruse with the optical assemblies described herein. The optical assembliesinclude at least a first filter stack, a second filter stack, a lens,and a display panel. The first filter stack and the second filter stackmay be flat, non-curved elements. The first filter stack and the secondfilter stack may be parallel to the lens and the curved lens and thelens may be aligned on an axis common to the curved lens and thedisplay. The curved lens may be composed of plastic and coated with abeam-splitting layer including a positive mirror surface configured toresolve display pixels.

The process 1400 may include receiving (1402) image content from adisplay toward a first filter stack and transmitting (1404) a portion ofthe image content through a curved lens parallel to the optical axis ofa lens. The portion of the image may be partially reflected andpartially transmitted after passing through the curved lens and to asecond filter stack. The partially transmitted portion may change (1406)polarized handedness from right hand circularly polarized to left handcircularly polarized during transmission. The partially transmittedportion may be transmitted (1408) through the second filter stack andprovided to the lens for viewing by a user.

In some implementations, the process 1400 may include optical assembliesin which the first filter stack includes a first linear polarizercoupled to a first quarter wave plate, the second filter stack includesa second quarter wave plate coupled to a polarizing beam splitter thatis coupled to a second linear polarizer, and the curved lens includes aplastic lens with a beam splitter coating. The curved lens may bedisposed between the first filter stack and the second filter stack.

In some implementations, the HMD devices described throughout thisdisclosure 1000 may be adapted to include or house an emissive displaysuch as a Cathode Ray Tube (CRT), a Field emission display (FED), aSurface-conduction Electron-emitter Display (SED), a Vacuum FluorescentDisplay (VFD), an Electroluminescent Displays (ELD), a Light-EmittingDiode Displays (LED), a Plasma Display Panel (PDP), an ElectrochemicalDisplay (ECD), a liquid crystal on silicon (LCOS) display, or an OrganicLight Emitting Diode (OLED). In some implementations, the HMD device 102may be adapted to include non-emissive displays including an LCD devicewith light sources being RGB, LED, or white LED.

In particular implementations, the systems and methods described hereincan include one or more optical assemblies ranging from about 2 to about3 inches both width and length and from about 1 to about 3 inches indepth. Other variations are possible.

Example Filter Stack Assemblies

Example filter stack assemblies are shown below. Although specificdimensions and layers are provided, other variations in such dimensionare possible. In general, the filter stacks described herein are thinenough that very little image degradation occurs. In addition,magnification lenses may suffice without redesigning or readjustingbased on different levels of tilting in the versions that providetilt-able components.

A first example filter stack is shown below as Example Filter Stack I.The example filter stack includes a substrate/cover glass layer that mayinclude an affixed beam splitter or a free standing beam splitter. Insome implementations, the beam splitter may be a coating on the quarterwave plate. The example filter stack also includes the quarter waveplate adhered with pressure-sensitive adhesive to a linear polarizer,which can be adhered to a substrate or cover glass layer. The examplethickness are shown below for each component with a final first filterstack (e.g., filter stack 206) having an assembled thickness of about1.243 millimeters. In some implementations, filter stack 206 includes asubstrate/cover glass (Row 1 below) with a beam splitter coating and asecond substrate/cover glass (Row 7 below) with an antireflectivecoating.

Thickness # Layer Comment (mm) 1 B270/D263 Glass/BS Substrate/Coverglass & Beam 0.21 splitter Coating 2 PSA Pressure-sensitive adhesive0.025 3 QWP Quarter waveplate film 0.073 4 PSA Pressure-sensitiveadhesive 0.025 5 LP Linear polarizer film 0.185 6 PSA Pressure-sensitiveadhesive 0.025 7 B270/D263 Glass Substrate/Cover glass & Coating 0.7=1.243

Example Filter Stack I

A second example filter stack is shown below as Example Filter Stack II.The example filter stack includes a substrate/cover glass layer that mayinclude a linear polarizer film adhered with pressure-sensitive adhesiveto a wiregrid polarization beam splitting film. The beam splitting filmmay be adhered in the same manner to a quarter wave plate film. Thequarter wave plate may be adhered to a linear polarizer, which can beadhered to a substrate or cover glass layer. The example thicknesses areshown below for each component with a final second filter stack (e.g.,filter stack 208) having a thickness of about 1.458 millimeters. In someimplementations, the filter stack 208 includes substrate/cover glasslayers that have an antireflective coating (i.e., in both Rows 1 and 9below).

Thickness # Layer Comment (mm) 1 B270/D263 Glass Substrate/Cover glass &Coating 0.7 2 PSA Pressure-sensitive adhesive 0.025 3 LP Linearpolarizer film 0.185 4 PSA Pressure-sensitive adhesive 0.025 5 WGFWiregrid Polarization Beam 0.19 splitting film 6 PSA Pressure-sensitiveadhesive 0.025 7 QWP Quarter waveplate film 0.073 8 PSAPressure-sensitive adhesive 0.025 9 B270/D263 Glass Substrate/Coverglass & Coating 0.21 =1.458

Example Filter Stack II

A third example filter stack is shown below as Example Filter Stack III.The example filter stack may be stacked near or adjacent to a curvedbeam splitter and/or lens. That is, the curved beam splitter may be afree standing beam splitter. The filter stack may include a quarter waveplate film adhered to a linear polarizing film that is adhered on theopposite side to a substrate/cover glass layer. The layers may beadhered with pressure-sensitive adhesive, or by another method. Theexample thickness are shown below for each component with a final firstfilter stack (e.g., filter stack 406) having an assembled thickness ofabout 1.848 millimeters. In some implementations, the filter stack 406includes substrate/cover glass layers that have an antireflectivecoating (i.e., in both Rows 1 and 7 below).

Thickness # Layer Comment (mm) 1 B270/D263 Glass Substrate/Cover glass &Coating 0.5 2 CBS Curved Beam Splitter/Lens 0.34 3 QWP Quarter waveplatefilm 0.073 4 PSA Pressure-sensitive adhesive 0.025 5 LP Linear polarizerfilm 0.185 6 PSA Pressure-sensitive adhesive 0.025 7 B270/D263 GlassSubstrate/Cover glass 0.7 =1.848

Example Filter Stack III

A fourth example filter stack is shown below as Example Filter Stack IV.The example filter stack includes a substrate/cover glass layer that mayinclude a linear polarizer film adhered with pressure-sensitive adhesiveto a wiregrid polarization beam splitting film. The beam splitting filmmay be adhered in the same manner to a quarter wave plate film. Thequarter wave plate may be adhered to a linear polarizer, which can beadhered to a substrate or cover glass layer. A beam splitter (e.g., lens408) may be inserted between Example Filter Stack III and Example FilterStack IV. The example thicknesses are shown below for each componentwith a final second filter stack (e.g., filter stack 410) having athickness of about 1.458 millimeters. In some implementations, thefilter stack 410 includes substrate/cover glass layers that have anantireflective coating (i.e., in both Rows 1 and 9 below).

Thickness # Layer Comment (mm) 1 B270/D263 Glass Substrate/Cover glass0.7 2 PSA Pressure-sensitive adhesive 0.025 3 LP Linear polarizer film0.185 4 PSA Pressure-sensitive adhesive 0.025 5 WGF WiregridPolarization Beam 0.19 splitting film 6 PSA Pressure-sensitive adhesive0.025 7 QWP Quarter waveplate film 0.073 8 PSA Pressure-sensitiveadhesive 0.025 9 B270/D263 Glass Substrate/Cover glass 0.21 =1.458

Example Filter Stack IV

In any of the filter stacks described herein, the polarizer layer/film(e.g., LP) may be outside of a filter stack. For example, the polarizerlayer may be laminated on or within a display module. If for example,the display includes a polarizer layer (i.e., as in a pre-polarizeddisplay), the polarizer layer is not needed.

As used herein, and unless the context dictates otherwise, anydiscussion of tilting, orienting, or direction with respect tocomponents described in this disclosure generally pertains to movingsaid component from a normal direction to the plane of a verticallyplaced component within an HMD device, for example. Namely, movingcomponents described in this manner can pertain to moving the componentwith respect to the optical axis of particular lenses used in theassemblies.

As used herein, and unless the context dictates otherwise, the term“coupled to” is intended to include both direct coupling (in which twoelements that are coupled to each other contact each other) and indirectcoupling (in which at least one additional element (including airgap) islocated between the two elements).

Various implementations of the systems and techniques described here canbe realized in digital electronic circuitry, integrated circuitry,specially designed ASICs (application specific integrated circuits),computer hardware, firmware, software, and/or combinations thereof.These various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms “machine-readable medium”“computer-readable medium” refers to any computer program product,apparatus and/or device (e.g., magnetic discs, optical disks, memory,Programmable Logic Devices (PLDs)) used to provide machine instructionsand/or data to a programmable processor, including a machine-readablemedium that receives machine instructions as a machine-readable signal.The term “machine-readable signal” refers to any signal used to providemachine instructions and/or data to a programmable processor.

To provide for interaction with a user, the systems and techniquesdescribed here can be implemented on a computer having a display device(e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor)for displaying information to the user and a keyboard and a pointingdevice (e.g., a mouse or a trackball) by which the user can provideinput to the computer. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be any form of sensory feedback (e.g., visual feedback,auditory feedback, or tactile feedback); and input from the user can bereceived in any form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in acomputing system that includes a back end component (e.g., as a dataserver), or that includes a middleware component (e.g., an applicationserver), or that includes a front end component (e.g., a client computerhaving a graphical user interface or a Web browser through which a usercan interact with an implementation of the systems and techniquesdescribed here), or any combination of such back end, middleware, orfront end components. The components of the system can be interconnectedby any form or medium of digital data communication (e.g., acommunication network). Examples of communication networks include alocal area network (“LAN”), a wide area network (“WAN”), and theInternet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the specification.

In addition, the logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. In addition, other steps may be provided, or steps may beeliminated, from the described flows, and other components may be addedto, or removed from, the described systems. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A method comprising: receiving image content froman emissive display toward a first filter stack, the first filter stackbeing oriented in a first direction from an optical axis of a firstlens, and toward the first lens; transmitting the image content througha curved lens having an optical axis that is parallel to the opticalaxis of the first lens, wherein the curved lens transmits a portion ofthe image content to at least one optical element and to a second filterstack, the second filter stack being oriented in a second direction fromthe optical axis of the first lens, the first direction corresponding toa non-zero tilt of a normal direction of the first filter stack to afirst angle with the optical axis, and the second directioncorresponding to a non-zero tilt of a normal direction of the secondfilter stack to a second angle with the optical axis, and wherein thefirst angle is larger than the second angle; and receiving the portionfrom the second filter stack and providing at least some of the portionto the first lens, wherein the portion changes polarization handednessfrom right hand circularly polarized to left hand circularly polarizedupon passing through the curved lens and the at least one opticalelement.
 2. The method of claim 1, wherein: the first angle is about 5to about 13 degrees off of a vertical offset from the optical axis ofthe first lens and toward the first lens; and the second angle is about5 degrees off of the vertical offset from the optical axis of the firstlens.
 3. The method of claim 1, wherein the first filter stack isparallel to the emissive display.
 4. The method of claim 1, wherein thecurved lens is composed of plastic and coated with a beam splitterlayer.
 5. The method of claim 4, wherein the beam splitter layerincludes positive mirror surface configured to resolve display pixels.6. The method of claim 1, wherein the at least one optical elementcomprises two or more optical lenses adapted to reduce opticalaberrations.
 7. The method of claim 1, wherein: the first filter stackis a first standalone assembly that includes a first linear polarizercoupled to a first quarter wave plate; the second filter stack is asecond standalone assembly that includes a second quarter wave platecoupled to a polarizing beam splitter that is coupled to a second linearpolarizer; and the curved lens includes a lens with a beam splittercoating, the curved lens being disposed between the first stand aloneassembly and the second standalone assembly.
 8. A system comprising: afirst standalone assembly that includes a first linear polarizer coupledto a first quarter wave plate; a second standalone assembly thatincludes a second quarter wave plate coupled to a polarizing beamsplitter that is coupled to a second linear polarizer adjacent to anon-curved lens; and a curved lens with a beam splitter coating, thecurved lens being disposed between the first stand alone assembly andthe second standalone assembly, wherein the first standalone assembly isoriented in a first direction, the second standalone assembly isoriented in a second direction, the first direction corresponding to anon-zero tilt of a normal direction of the first standalone assembly toa first angle with an optical axis of the non-curved lens, and thesecond direction corresponding to a non-zero tilt of a normal directionof the second standalone assembly to a second angle with the opticalaxis of the non-curved lens, and wherein the first angle is larger thanthe second angle.
 9. The system of claim 8, wherein the beam splittercoating includes a positive mirror surface configured to resolve displaypixels.
 10. The system of claim 8, wherein the system further comprisesat least one optical element including two or more optical lensesadapted to reduce optical aberrations.
 11. The system of claim 8,wherein the system further includes at least one positive refractiveelement to balance a field of curvature for the system.
 12. The systemof claim 8, wherein the curved lens is non-rotationally symmetrical. 13.A head-mounted display housing comprising: at least one optical assemblyincluding a curved beam splitter device disposed between a first filterstack and a second filter stack; an image projecting device adapted tobe seated at a plurality of angles within the head-mounted displayhousing; and at least one lens; and wherein the first filter stack isoriented in a first direction, the second filter stack is oriented in asecond direction, the first direction corresponding to a non-zero tiltof a normal direction of the first filter stack to a first angle with anoptical axis of the at least one lens, and the second directioncorresponding to a non-zero tilt of a normal direction of the secondfilter stack to a second angle with the optical axis of the at least onelens, the first angle being larger than the second angle.
 14. Thehead-mounted display housing of claim 13, wherein the image projectingdevice is seated at a tilt angle selected based on the first angle orthe second angle.
 15. The head-mounted display housing of claim 14,wherein the tilt angle comprises more than 5 degrees and less than 25degrees of a vertical offset from the optical axis of the at least onelens.
 16. The head-mounted display housing of claim 13, wherein a tiltof the first filter stack or the second filter stack results inmodifying a field of view associated with the head-mounted displayhousing, the modification including moving image artifacts outside ofthe field of view.
 17. The head-mounted display housing of claim 13,further comprising a plurality of optical elements disposed between thefirst filter stack and the second filter stack, the plurality of opticalelements configured to decrease optical aberrations.
 18. Thehead-mounted display housing of claim 13, wherein the at least one lensprovides a focal length of about 13 millimeters to about 20 millimeterswithin the head-mounted display housing.
 19. The head-mounted displayhousing of claim 13, wherein the first filter stack includes a firstlinear polarizer coupled to a first quarter wave plate and the secondfilter stack includes a second quarter wave plate coupled to apolarizing beam splitter that is coupled to a second linear polarizer.20. The head-mounted display housing of claim 13, wherein thehead-mounted display housing includes two optical assemblies, eachconfigured to provide image content to the at least one lens incorresponding left and right eyepieces associated with the head-mounteddisplay housing.